The present invention relates to web printers of the type that form images on webs carried at high speed.
In the general types of printers that form, images on webs, pin members of a tractor mechanism mounted on the printer are engaged with the feed holes disposed along the edges of the web, and the tractor mechanism is driven to feed the web as an image is formed thereon using the image forming section of the printer. After the web with the feed holes has been printed, however, the portions of the web along which these feed holes are disposed (usually along the left and right edges of the web) need to be cut off, and thus an increased time is spent after printing in obtaining the final printed matter. Also, the printer itself requires a tractor mechanism as a component thereof, which inherently results in a complex configuration. Such a cutting operation as mentioned above can be omitted by adopting webs that are free of feed holes, using a web feed roller mechanism instead of a tractor mechanism of the printer.
In this regard, for a printer that uses webs that are free of feed holes and which forms an image on a web while feeding it by use of a feed roller mechanism, if this printer is of the type which operates in no higher than a middle-speed region in which only about 50 pages per minute are printed on A4-paper on a horizontal feed basis, printing not conspicuous in terms of print position offsets is possible since not too significant slipping occurs between the web and the feed rollers. If, however, the printer is of the high-speed type that is capable of printing more than 100 pages per minute or is of the ultrahigh-speed region type capable of printing more than 200 pages per minute, it is difficult with a conventional configuration to feed the web to the image forming section accurately; and, even when extremely thin paper, such as is often used for a dictionary, for example, is fed at a rate as high as more than 100 pages per minute, the need arises to very accurately control the tension, traveling position, etc. of the web being fed.
The object of the invention is to provide a printer that, irrespective of the web type, enables stable feed of the web at high speed and with high accuracy.
The object set forth above can be achieved by providing a printer having a buffer for adjusting the traveling position of the web under its slack status, a tension assigning unit for assigning fixed tension to the web delivered from said buffer, a device for detecting the traveling position of the web delivered from said tension assigning, a skew correction unit for adjusting the skew of said web according to the output from said detection unit, and an image forming unit that forms images on the web delivered from said skew correction unit.